Graphite bodies which are to be used as electrodes generally require a protective coating of an electrically conductive metal or metal oxide to prevent the rapid errosion of the graphite body by an electric arc. It has been found that, rather than a thick coating of a single metal, several relatively thin coatings of different metals or other substances applied to the graphite body afford better protection thereof.
Devices for producing coated graphite bodies are known and usually comprise a machine having a base on which is provided a turret for rotatably supporting the graphite body to be coated. Also provided on the base is a carriage movable in a longitudinal direction alongside the rotating body and carrying the coating tools and an electrode for forming an electric arc with the graphite body which will bond the coating thereto, the carriage being further provided with a trailing cable which supplies the electric current, air and water needed on the carriage for performing the coating operations.
If the coating applied to the body is to be of even thickness, or a specific thickness, the relative movement between the rotating body and longitudinally advancing carriage must be carried out in a perfect sequence, which makes the known devices of this kind extremely complicated.
Another disadvantage of present coating machines is that if the coating is to be multilayered, the graphite workpiece must be moved to a different machine for each layer applied, so that the body must be repositioned by being clamped and unclamped in each of the turret mountings, causing delays in the coating operation, further compounded by the carriages having to return to a starting position without performing any work.